Pulse width discriminator circuit



Sept. 2, 1952 e. B. GUTHRIE, JR 2,609,501

PULSE WIDTH DISCRIMINATOR cmcun- Filed Jan. 5, 194s FIG. I

FIG. 2

VOLTAGE I AT A TERMINA I l VQLTAGE AT 8 Tp WIRE 29 A VOLTAGE GRID I9 I I VOLTAGE I I i PLATE 3? I A I GEORGE E. GUTHRIE,JR.' 1 BY "I Arromfri to the operation of the circuit.

Patented Sept. 2, 1952 by-mesne assignments, to the United States of Americaas represented by the Secretary of War Application January 3, 1946, Serial No. 638,892

1 This inventionrelates generally to electrical circuits and more particularly to pulse length discriminator circuits.

It is often desirable to prov-idea circuit which will accept a pulse of a certain critical length jorfgreateii but will reject a pulse whose length is less-than the critical value. It is also desirable to providesuch a circuitwhich is insensitive to" the amplitude of the pulse. One application of such a circuit is in radio beacon'systems.

It is an object of this invention, thereforato providea circuit which will accept pulses of a critical length or greater and reject pulses whose length is less than the critical value.

It isa further object of this invention to provide a pulse length discriminator which is-ine sensitive to pulse amplitude. In general this invention comprises two triodes which substantially subtract the incoming pulse from an integrated waveform generated by the pulse. An output pulse is obtained'only when the incoming pulse is of sufiicient durationto permit the integrated wave to rise to a critical value. d

Other objects, features and advantages of this invention will suggest themselves to those skilled in the art and will become apparent from the following description of the invention taken in connection with the accompanying drawing in which H T Fig. 1 is a schematic circuit diagram of this invention; and g Fig. 2 shows a group of waveforms relating Referring now more particularly .to Fig. I, the input terminal I] connects to gridl3' of vacuum tube l5 through arm I6 of potentiometer l1 and also to grid IQ of vacuum tube 2| through resistorv 23. Potentiometer l1 connects between terminal I! and ground. Cathode of tube 15 and cathode 21 of tube 2| are electrically connected by lead 29. Resistor 3| and capacitor 33 are connectedbetween lead 29 and ground and are connected in parallel with each other. Plate 35 of tube I5 is connected to a source of positive potential. Plate 3'! of tube 2| is connected to a source of positive potential through resistor 39. Capacitor 4| is connected between grid l9 and ground.

Fig. 2A is the voltage waveform at terminal I I. Fig. 2B is the voltage waveform at the lead 29. Fig. 2C is the voltage waveform at grid 19. Fig. 2D is the voltage waveform at plate 31. Fig. 2E will be described later.

In operation, substantially rectangular posi- 5.-Clairns.' (01'. 250-27) tive pulses are applied between terminal II and ground. Circuit constants are so chosen-that tube 15 is normally conducting and tube 2| is ing voltage across resistor 3!. The amplitude of the input pulse appearing at grid l3'is determined by the setting of potentiometer 'l'l. A positive pulse appears at lead 29 as shown in Fig. 213 due to cathode follower action." The leading edge is exponential due to oapacitor '33 charging through the'plat'e resistance of tube I5.

The trailing edge is also exponential due to the discharging of capacitor 33 through resistor 3|. This voltage appears at the cathodes 25 and'21: The voltage waveform at the grid I9-is 'anintegration of the input pulse due to the charging and discharging of capacitor 4| through resister 23. Therefore the grid Ill-groundvoltage is essentially an integration waveform of the input pulse while-the cathode 2'l--ground voltage is essentially a rectangular pulse with an exponential taiL'theamplitudeof this pulse being somewhat less than the input pulse and the amplitude being determined by the setting of the potentiometer l1 and the gain of thecathode follower tube l5. -It Will be obvious then that the cathode 2'I-ground voltage is effectively subtracted from the grid l9ground volt-'- age and so long asthe amplitude of grid l9-+ ground integrated-waveform is less than the cathode Ti -ground rectangular waveform the tube 21 will remain in a nonconducting state. However, when the integrated waveform rises above the amplitude of the rectangular wave-'- form the tube 2| will conduct and a negative pulse and to is equal to the time for the inte-' grated wave to reach an amplitude equal to the rectangular wave, it-will be seen that when-ti; is equal to-or greater than to, a signal will ap pear at the plate 3'1. However, if in 'S-less than its, as shown in Figflf 2E, no signalwill ap'p'earfat the plate 31. 1 It will be seen that as an input pulse of a given time duration varies in amplitude, the waveforms at the grid I9 and'gcathode 21 vary in amplitude proportionally and the relationships t and to do not change. Therefore, pulse length discrimination is substantially independent of pulse amplitude.

For proper operation of the circuit, the time constant of the trailing edge of the cathode 2'!ground waveform is, in practice, at least as great as the time constant of the trailing edge proved byih'aving the-exponential trailing "edge on the waveform impressed on the cathode 2'Iground circuit since this portion of the" waveform essentially cancels out .the discharge portion of the integrated waveform.

deriving an output pulse from said amplifier stage in response to an integration waveform pulse having an amplitude exceeding the amplitude of the pulse waveform across the said cathode circuit of said amplifier stage.

3. A pulse with discriminator circuit comprising, first and second vacuum tubes each having atleast a; cathode, control gridmand anode, a cathode loadilcircuit commonatozboth tubes, an

integrating circuit connected to the control grid .Cof said second tube, means for simultaneously applying an. input, pulse signal to the control grids of said first andsec'ond tubes, and means for deriv- It will be seen that the circuit.hereinesetiforth will accept only pulses of.-a critical length;or.

greater, the acceptance being' lindependentliof' Therefore, it will be ,unnecessary to have a signal limiting stage before the pulse amplitude.

discriminator.

While there has been described what is at present considered to be the preferred embodiment of this invention, it willbe obvious tothose skilled in the art that various changes and modifications may be made therein without-departing from the scope of the invention as set forth in the appended claims and I- claim all such changes and modifications as fall:fairly within the spirit and-scope of the invention.

, What is claimedis:

1. In a pulsediscriminator circuit, a first vacuum tube' having at least, a cathode, acontrol grid, andeplate, means: for applying a pulse signal :to the-control grid of 1 saidfirst tube from a source external to :said :circuit; a potentiometer connected between said :means andground, the arm tof=-said potentiometer being connected to the grid ofsaid first tube, a first'resistive means conhecting the cathode ofsaid first tube to ground, a first :capacitivemeans connecting saidcathode 'of-saidfirst tube to ground,-means connecting -theplate ;-of said first tube to a'source of;positive: potential, a second vacuum tube having-at leasta cathode, controljgrid, and plate, means connecting said cathode of said first-tube tothe cathode; :of said second tube, a second .resistive .means connecting the source oflthe input pulses tozthe grid of said second tube, a second capacitive means connecting saidgrid of said: second tube to -ground,'and a third resistive means-connecting the plate of "saidisecond tube to a-source :ofv positivecpot'ential.

":2. =A':pulsewidth discriminator. circuit comprising, acathode follower stage having a control grid, =an amplifier stage having a control grid, said-stages having a common cathode biasing circuit, means for rendering said-cathode follower stage normally conducting and said amplifier stage biased substantially to cut-ofi, resistive means'forsimultaneously applyinga pulse signal to said control grids, capacitive means connecting said amplifier stage control grid .to ground, whereby the application of an input pulse ,causesasimilar pulse to be impressed acrossthe said amplifier cathode circuit and an integration waveform of (the, input pulse to be impressed 'on :thegrid-ofsaid amplifier stage, and meansfor in g anvoutputsignal from said second tube in response-.tmaninput pulse signal having more than iatpredetermined duration.

A A pulse width discriminator circuit comprising a cathode "follower circuit and a normally non-conducting amplifier each having a cathode and control grid, a load circuit for said cathode followencoupledbetween the grid of. said amplifier andboth cathodes, meansfor. simultaneously impressing a positive-goingpulse signal'onsaid control grids, a first integrating means-including said load circuit for integrating theoutput, pulse signal of the cathode follower, asecondintegrating'means coupled to the grid. of :said amplifier for integrating the pulse signal impressed on the amplifier-control grid, said first integrating means having afaster charging rateand a-slower discharging rate than said second integrating means, whereby an output signal is producedby said amplifier when a predetermined voltagezrelation between the outputs of .said first .andsecondintegrating means igreached.

, 5. A pulse-width discriminator circuitcomprising means for producinguasfirst:output voltage pulse when tan-input voltage rpulse isnapplied thereto, a circuit coupled to. said .pulseproducing means for. integrating said firsteoutput voltage pulse toproduce a second-output voltage pulse, means for integrating said input voltage pulse-to produce a third output voltage pulserandsnormally inoperative switch means receptive of-both said second and third output voltage, pulses and responsive only: to .a predetermined voltagedifference betweenrsaid'second and third output voltage pulses, said integrating circuit havinga time .;constant .thatis small. relative to,- that. of said means for integrating.

REFERENCES vcrren The following r'eferences are ofqrecord-initthe :file ,ofxthispatentz UNITED STATESPATENTS Number i Name L'Date 2,275,930 lTor'cheuxws Mar. =10,v 1942 2,287,926 Zepler. a..- a June 30,1942 2,405,843 .Moe. m--- Aug..-13, 1946 2,438,910 Grieg Apr.' 6,1948

FOREIGN PATENTS Number Country Date 528,192 GreatBritain "Oct;24,'"I9i40 

